The present invention concerns a method of surface treatment for the protection and functionalization of polymers (synthetic organic plastic materials). It renders the surface of a plastic material less sensitive to the environment, sets up a physical and/or chemical protective barrier, and enables the production of electronic or optoelectronic components on a polymer substrate. It is particularly useful for creating scratchproof protection, optical filtration functionalities, and barriers to water vapour or oxygen for example. It also permits the production of display screens. It can be used, but not exclusively, in the field of windows when organic materials are used to replace glass, in particular for automobiles. A polymer product obtained according to the method is also claimed.
Methods are known by which the surface of a metal or glass material is protected by depositing one or more layers of silicon alloys, for example silica. It has been observed that the silica deposit is more adhesive, homogenous and non-porous when the substrate temperature is high during the deposit.
In addition to the protective effect of the silica, optical effects may be obtained by stacking layers of silicon alloys with different refractive indexes. These optical effects are especially optical filtration effects.
These inorganic materials are relatively heavy and do not readily lend themselves to the production of complex, pliable or flexible shapes. It is thus increasingly desirable to replace them by polymers with equivalent optical properties but which are lighter and simpler to use. However, known polymers generally have even poorer surface resistance properties against environmental chemical and/or physical attack. In particular, these are easily scratched. It has thus been proposed to protect the surfaces of these materials by the production or application of a protective layer. With this objective, one (or more) protective layers with a thickness of a few micrometers must be deposited. This layer must adhere durably. It is observed that for a layer thick enough for good anti-scratch protection, the adhesion is a critical parameter.
The invention thus concerns a method for treating surfaces for protection and functionalization of polymers, by gas plasma deposit in a confined chamber of at least one layer of a silicon alloy.
According to the invention,
the silicon alloy is selected from silicon, and its oxides, nitrides and oxynitrides;
a pre-treatment of the surface with plasma is performed in the same chamber before depositing the silicon alloy, this pre-treatment consisting of a surface treatment comprising etching (or ablation) of a surface zone of the polymer and a step of depositing a polymeric carbon compound.
The term alloy signifies a combination between silicon and one or more other atoms but must also be considered here as signifying silicon alone. The silicon oxides may be of type SiOx including silica (x=2) and the nonstoichiometric silicon oxides (xxe2x89xa02). The deposit is performed at a temperature lower than the degradation temperature of the polymer. The polymer degradation temperature corresponds to a temperature at which the material softens or begins to melt or even burn, and more generally to a temperature at which the material loses its properties of use. It is thus not in general necessary specifically to heat the material in this method. If however heating is necessary, this may be performed to a temperature lower than the degradation temperature of the material.
By polymeric carbon should be understood a highly hydrogenated (at least 10% hydrogen by atomic percentage) amorphous carbon, with low optical index and high energy gap (3 to 5 eV). For example, the material listed in table 1 (a-C:H 1) has an index of 1.59 (2 eV), a hydrogen concentration of 56% and a density of 1.2 g/cm3.
In various embodiments of the invention, the following means, optionally combined according to all the technically feasible possibilities, are used:
the surface treatment is performed first, followed by the deposit of the polymeric carbon compound;
the step of depositing the polymeric carbon compound is begun before the end of the surface treatment;
the preparation is obtained by the action of a plasma generated from an oxidizing gas. The oxidizing gas may, for example, be chosen from oxygen and N2O;
the etched thickness of the surface zone is between 20 angstroms and 3000 angstroms;
the etched thickness of the surface zone is between 100 angstroms and 900 angstroms and is preferably approximately 500 angstroms;
the carbon compound deposit is obtained by the action of a plasma generated from a carbon-containing gas, the carbon-containing gas being chosen from methane, ethane, butane, propane, pentane, hexane and their mono or poly-unsaturated derivatives including ethylene and acetylene;
the thickness of the carbon compound deposit is between 30 angstroms and 130 angstroms and preferably between 50 angstroms and 100 angstroms;
the deposited carbon compound is a hydrogenated carbon in amorphous form;
the polymer is a polycarbonate;
the polymer is selected from the polymethyl methacrylates, the polyethylenes, the polypropylenes, the polyethylene terephthalates;
the untreated polymer is treated directly in the chamber;
several layers of silicon alloys are deposited, for example to obtain one or more optical effects;
the plasma reactor is selected from the microwave or radiofrequency reactors including the electron cyclotron resonance reactors, the distributed electron cyclotron resonance reactors, and the cathode sputtering reactors. The cathode sputtering reactors are also called xe2x80x9ctargetxe2x80x9d reactors.
the plastic material is a polycarbonate, the thickness of the layer of amorphous hydrogenated carbon is between 50 angstroms and 100 angstroms and a single layer of silica with thickness between 1 and 7 xcexcm and preferably about 5 xcexcm is deposited.
The invention also concerns a polymer product which has been subjected to a surface treatment for protection and functionalization.
According to the invention, the polymer treated according to any of the embodiments of the method defined above contains on its surface a prepared zone and a layer of amorphous carbon overlaid with one or more layers of one or more silicon alloys.
This method can be used to produce layers for protection and functionalization on surfaces of polymers of different shapes, the layers being durable and strongly adhesive compared to known methods. The term protection corresponds to any protection, alone or in combination, against mechanical attack, for example scratches, optical attack, for example ultraviolet, and also possibly chemical attack.
Since the plasma treatment enables large surface areas to be treated, and the steps of the method of the invention all take place in the same chamber without breaking the vacuum and without any heating of the material being necessary, high yields may be obtained. The method of plasma deposit also makes it possible to produce optical components by stacking of layers with different indexes, either with sudden rise in indexes, or by continuous variations in the indexes, or even a combination of the two. The possibility of producing an optical filter may, for example, allow protection of the bulk of the plastic material from ultraviolet radiation and thus to increase its lifetime.
In addition to the application to automobile windows, other applications are anticipated for the invention, in particular all applications where glass may be replaced by a polymer, for example the optical windows of light projectors and large-area electronic components based on a thin layer of plasma-deposited silicon. In all these applications, the polymer or plastic material is essentially selected for its lightness and optical transparency when replacing glass. The polymer may also be chosen for its advantageous mechanical properties compared to glass and particularly its ability to be bent or deformed.
The method and the plastic material treated according to the invention may have other applications, for example in the production of flexible packaging from plastic material or casings, for example for the barrier properties of the silica and, in particular, against the diffusion of water vapour and/or oxygen.
Finally, the implementation of the method is extremely simple and does not require the use of a fundamentally new plasma reactor. The method in fact can be used with any gas plasma reactor for depositing silicon alloys by simply providing for an inlet for an additional gas which is a carbon-containing gas.